Vaccines designed to protect against malaria by inducing CD8+ cytotoxic T lymphocytes (CTL) in individuals of diverse HLA backgrounds must contain multiple conserved epitopes from various preerythrocytic-stage antigens. Plasmodium falciparum sporozoite surface protein 2 (PfSSP2) is considered an important antigen for inclusion in such vaccines. Therefore, we investigated the presence of anti PfSSP2 CTL in two HLA-B8+ volunteers immunized with irradiated P. falciparum sporozoites and characterized their CTL responses using PfSSP2-derived 15-amino acid peptides bearing the HLA-B8 binding motif. Of the five HLA-B8 motif-bearing 15-mers identified in the PfSSP2 sequence, two peptides sharing a 10-amino acid overlap sensitized HLA-B8 matched target cells from both volunteers for lysis by peptide-stimulated effectors. The identification of two HLA-B8 restricted CTL epitopes on PfSSP2 provides data critical to developing an epitope-based anti-liver stage malaria vaccine. MHC class II molecules can exist in two conformations that can be distinguished on the basis of their stability in SDS. The formation of SDS-stable dimers has been shown to correlate with persistent expression of antigenic MHC class II-peptide complexes by murine antigen-presenting cells. HLA DR molecules contain either a Val or a Gly at position 86 of the beta chain, which is located in a conserved and prominent hydrophobic pocket in the peptide binding site. We showed that VAL86-containing DR molecules more frequently select peptides which induce the formation of SDS-stable dimers than Gly86 variants. The definition of the requirements for the formation of SDS-stable HLA class II molecules may beimportant for the design of effective peptide-based immunomodulation protocols. We purified a DNA binding protein that recognizes a portion of the MHC class I regulatory element region 1/NF-kappaB binding site whose expression correlates with the expression of a MHC class I transgene in the thymus and showed it to be the RBP-Jkappa protein, also known as the EBV C-promoter binding factor CBF1. Although RBP-Jkappa/CBF1 is ubiquitously expressed, only the thymic nuclear extract showed strong DNA binding activity with probes containing the NF-kappaB recognition sequences present in the MHC class Ia, IL-2Ralpha, and granulocyte- macrophage CSF promoters. Thus, RBP-Jkappa/CBF1 in thymic extracts demonstrates a clearly distinguishable DNA binding specificity that correlates with tissue-specific expression of a class I transgene. This, coupled with the fact that our previous study showed enhanced expression of the transgene in CD4+CD8+ thymocytes,suggest that RBP-Jkappa/CBF1 may play a role in the development of the immune system.